(a) Field of the Invention
The present invention relates to a liquid crystal display capable of controlling luminance of a backlight, and more particularly to a method of controlling the luminance of a backlight in close relation to image data for improving visibility of a moving picture.
(b) Description of the Related Art
In recent years, display devices for personal computers and television sets are required to be light-weighted and slim. Flat panel displays such as a liquid crystal display (LCD), which satisfies such requirements, instead of a cathode ray tube (“CRT”) are developed and put into practice in a variety of fields such as a display device for computer, a liquid crystal television.
An LCD includes a panel having a plurality of pixels arranged in a matrix and a panel opposite thereto. Liquid crystal material with anisotropic dielectric is interposed between the panels. An electric field is applied therebetween, and a desired image is displayed by adjusting the strength of the electric field to control the amount of light passing through the panels.
An LCD used for a television set is required to display moving pictures rather than still pictures. However, the LCD is disadvantageous in displaying the moving picture due to its display characteristics. For example, a voltage is applied for a part of one frame, i.e., one horizontal period to generate an electric filed, which is applied to the liquid crystal to respond thereto substantially in the horizontal period and to remain its state during one frame. When the strength of the electric field is changed upon the change of the frames, a drag phenomenon occurs on screen of the LCD due to a long response time of the liquid crystal. That is, the display characteristic of the LCD for the moving picture is inferior due to the long response time of the liquid crystal. Thus, such image characteristic of the LCD needs to be improved for use in a television set, etc., which necessary processes a large amount of moving pictures. In recent years, a method of driving a backlight with a predetermined on/off duty ratio during a frame has been proposed like dot scanning of the television set.
In addition, a typical LCD keeps the luminance of the backlight constant regardless of gray levels of image data. When the image data with high gray levels is localized on a screen or most of the image data on a screen have high gray levels, appropriate luminance control of the backlight depending on the image data can improve the contrast of the display device. That is, it is required to control the backlight depending on the gray levels of the image data.
However, an LCD adapted to both the backlight control techniques has not been proposed, and the present invention relates to a method implementing both the two techniques in order to improve display characteristics.